Dengue fever and dengue hemorrhagic fever result from the infection with any of the four serotypes of dengue (DEN) viruses. These diseases have become a global public health problem, affecting 100 million people anually. Moreover, DEN viruses are potential bioterrorism agents since neither an effective treatment nor vaccine is available. Thus, research is needed to develop an effective and safe vaccine that will prevent infection and disease caused by any of these viruses. The objective of this study is to develop a DNA vaccine capable of inducing protective immune responses in rhesus macaques against DEN-2 virus infection. Our long-term objective is to develop a tetravalent DEN DNA vaccine. Our vaccine strategy is focused on the dengue envelope because this protein mediates the early binding and entry steps of infection. Neutralizing antibodies (Nab) against this protein were shown to be protective against pathogenic virus infection and disease. In this study we plan to evaluate immune responses generated in monkeys by our DNA vaccine candidate, Vec-D2 which encodes prM and env proteins of DEN-2, using four different vaccination regimens. Monkeys will be immunized with Vec-D2 either alone or absorbed onto polylactide-co-glycolide (PLG) microparticles, followed by the administration of an inactivated DEN-2 virus boost adjuvanted in MF59 or MF59 alone. Our hypothesis is that immune responses induced by Vec-D2 will be enhanced by coupling the plasmid DNA to PLG and that these responses could be further boosted by administration of inactivated virus in MF59. Immune responses will be monitored by ELISA, virus neutralization, CTL and proliferation assays. The level of protection induced by the different vaccine strategies against DEN-2 virus infection will be also ascertained: Complete protection will be determined by the absence of detectable viremia and of anamnestic immune responses. Results obtained from these studies will provide important information for the design and development of DNA vaccines expressing the envelope protein of DEN-l, DEN -3 and DEN-4.